Chapter 28: Plant Evolution and Classification Section one: Overview of plants
Adapting to Land • Nothing could live on land until 475 million years ago. • The Ozone layer developed, which offered protection from UV rays • 3 adaptations allowed plants to survive on land: • Preventing water loss • Ability to reproduce without water • Ability to absorb and transport nutrients
PreventingWater Loss • Plants had to go from having total exposure to water to the constant threat of evaporation. • Cuticle– a waxy covering on a plants surface that prevents water loss See any problems with this?
PreventingWater Loss • Stomata – Small openings in the surface which allow the exchange of CO2 and Oxygen. • They needed protection from evaporation that didn’t cut off their supply of CO2 Cuticle Stomata
Reproducing by Spores and Seeds • Plants had to develop reproductive structures that didn’t dry out. • Spores - • Seeds - Haploid reproductive cells surrounded by a hard outer wall – allowed for wide dispersal of plants An embryo surrounded by a protective coat. Some contained the tissueendospermwhich nourished the developing plant.
Absorbing and Transporting Materials • Some plants have Vascular Tissue – transports water and dissolved substances from one part of a plant to another. It also helps support the plant. It’s made up of two parts • When plants lived in water, they could absorb the materials around them • Plants needed a way to get the nutrients from the ground up into their entire structure. • Xylem– Carries water and inorganic nutrients FROM the roots TO the stems and leaves • Phloem– Carries organic compounds (carbohydrates) and some inorganic compounds to wherever the plant needs them.
Classifying Plants • There are 12 phyla of plants (used to be called divisions) • First they are separated based on if they are Vascularor Non-Vascular • Non-Vascular plants: No true vascular tissue, roots, stems or leaves • Vascular plants: Have vascular tissue, roots, stems and leaves
Vascular Plants • These can be further separated: Seedless vs. Seed plants • Seed plants can be even further divided: Gymnosperms and Angiosperms • Gymnosperms: Seeds are not enclosed into a fruit • Angiosperms: (Flowering plants) Produce seeds that are enclosed into a fruit
Alternation of Generations • Plants have a life cycle with two phases: • Sporophyteor diploid cycle: Spores produced • Gametophyteor haploid cycle: Gametes (Egg and sperm) produced • The plants will alternate between both cycles http://www.youtube.com/watch?v=jcWYAnmm-QE
Alternation of Generations • In Non-Vascular plants the gametophyte is the dominant stage. (Like in the video) • In Vascular plants, thesporophyteis the dominant stage. (example: Oak Tree)
In seed plants the gametophyte is usually is a very small parasite of the sporophyte. Example: gametophytes of flowering plants are microscopic parts of their flowers that aren’t photosynthetic. In seedless vascular plants the gametophyte is usually a separate small organism, that is really different from the sporophyte